1. Field
The present inventive concepts relate to apparatuses for monitoring physical properties of a substrate through detection of polarization properties of light, which is irradiated from a wide-area light source and is transmitted through or is reflected from a surface, and/or control methods thereof.
2. Description of the Related Art
In general, measuring optical properties of a material and/or thicknesses of thin films is important in the fields of, for example, physics, chemistry, and material science. Particularly, in the semiconductor industry, various nano-film fabricating processes are used, and in order to evaluate the physical properties of the fabricated nano films, ellipsometers, which employ a nondestructive and contactless real-time measurement technology, have been widely used as measurement equipment for processes.
With the development of light sources, light detectors, and computers, the performance of ellipsometers has been greatly improved, and in accordance with the development of processes using thin films, the application of the ellipsometers have been greatly increased.
The ellipsometers may be classified into a reflection type and a transmission type. Between the two types, the reflection type ellipsometer, which analyzes the polarization state of light that has an incident angle and is reflected from a surface of a test piece, has been widely used.
According to the reflection type ellipsometer technology, because parallel light is incident in a tilt direction, the incident angle can be accurately controlled. Thus, measurement is relatively accurate. However, if the size of incident beams is reduced through an iris, diffraction phenomenon may increase, and thus further reducing the size of the beams irradiated onto the test piece to mm or less may be challenging.
In the semiconductor industry, in order to evaluate various thin film fabricating processes for manufacturing semiconductor devices through measurement(s), a measurement region having a dimension of several tens of μm*several tens of μm is prepared on a wafer. In order to measure the physical properties of the measurement region, technology for focusing light on the surface of the test piece provided in the measurement region is used.
With the continuous development of semiconductor device fabricating technology, the size of a test piece patterned on a wafer is continuously reduced. Thus, the area of the limited measurement region is also reduced in proportion to the size of the test piece. However, in spite of intense research and effort, it has been difficult to further reduce the beam size of incident light due to technical barriers, for example, aberration and limitations of focal optical systems.
Recently, research has been made with respect to surface detecting ellipsometers, which measure the physical properties of a measurement region using the polarization properties of light irradiated from a wide-area light source and transmitted through or reflected from a surface.